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A Comparison of Techniques to Evaluate Plant Moisture Content for Earth and Space Applications. M.K. Corbett1, T.E. Foster2, C.R. Hall2, T.W. Dreschel, Ph.D.3 1Cornell University, Ithaca, NY, 2Dynamac Corporation, Kennedy Space Center, FL, 3National Aeronautics and Space Administration, Kennedy Space Center, FL.  

   The Porous Tube Plant Nutrient Delivery System can supply hydroponically grown plants with discrete amounts of water, influencing moisture content, which can affect physical characteristics of plants. The plant roots are provided with accurately controlled nutrient solution delivery with the intent to study how too much or too little water can stress plants and our ability to detect these stresses. Sensitive laboratory instruments, including a LI-COR 6400 Leaf Chamber Fluorometer and an Analytical Spectral Devices Spectrophotometer, were used to measure photosynthetic rate, fluorescence, water use efficiency and reflectance, all of which are influenced by the water status of plants. Minimal differences in these variables were expected to be detected. Physiological differences were found in plants grown at three different water availabilities. Plants found to have 83% leaf moisture (the -0.098 kPa treatment) showed the lowest photosynthetic rate and growth, and the highest non-photochemical quenching, while plants found to have 81.5% leaf moisture (the -0.98 kPa treatment) showed the highest photosynthetic rate and growth, the lowest non-photochemical quenching and were the healthiest in appearance. The equipment used in this study was sensitive enough to detect very small differences in plant characteristics influenced by leaf moisture contents that ranged from 79.9% to 83.0%.  

(Support: NASA, Dynamac Corporation, USDA)